28-08-2024, 10:43 AM
This brief paper is by Greg Goldstein and Ian Wilson
Increasing radio signal problems when flying at the PRCAC field at Toongabbie have occurred over the last 3-4 years, coincident with the rapid development of 5G telecommunications in Sydney. PRCAC members mostly fly planes, and in 2022 they used a wide range of radio equipment with the 2.4 Ghz band, with almost all major RC brands represented. Near PRCAC is an Optus phone tower adjacent to our field and 40m from the landing strip, that uses many frequencies including the 2.35 Ghz band. However other possible suspects for interference are numerous nearby factories with networked computers, and also networked vehicle fleets.
Apart from crashes due to loss of control, or temporary control glitches, pilots occasionally noticed their aircraft take an unexpected change of direction and asked: was that me? Pilots paid increased attention to improved antennas, and better rxs and power supplies without much effect. A few members tried the 900 Mhz band, using gear such as Frsky R9 and Frsky Tandem; they reported 900 Mhz gear solved the problems, but 900 Mhz never became popular at PRCAC.
Around Oct 2022 a trusted radio expert on Radio Control Groups said ELRS "is really a sea change in the available RF performance for 2.4 Gz systems and a major shot across the bows of the older solutions, especially for those of us flying in more challenging RF environments". This post and similar discussions on Radio Control Groups encouraged several PRCAC members to try ELRS, even though the general perception at the time was that ELRS was a drone radio.
In a nutshell: ELRS evolved because fpv drone pilots wanted to fly at long distances say 20 km and return safely. The ELRS developers discovered how to maintain a safe signal to noise ratio at a distance, and out of early prototypes such as Crossfire and Ghost there emerged ELRS. Turns out, the amazing signal to noise performance of ELRS is just what pilots of "fixed wing" (what drone pilots call airplanes) need at a 200 m distance to counter radio interference.
The ELRS early adopters at PRCAC experienced problems due to numerous differences between ELRS and commonly used radios such as Frsky or Spectrum; while each difference has a simple solution, there are around 6 to consider and address:
- running the Configurator on a computer to update tx or rx firmware.
- flashing tx or rxs with updated firmware using the internet and wifi; wifi is also used to set the tx and rx "bindphrase", which allows instant tx to rx binding when the tx and rx have a match.
- understanding the control and telemetry packets of the radio signal (see Notes below). For aircraft flown with line of sight, a packet rate 100 Hz, and a telemetry ratio of 1:32 are recommended.
- setting "dynamic power", so if interference corrupts the radio signal, the tx power immediately jumps say from 25 to 50 mw.(see Notes below)
- "arming" and channel 5 setting. Some think arming is only for drones, but that is not true. Dynamic power performance is enhanced if armed. (see Notes below)
- soldering wires onto rx boards. This was an early problem for some members, but now is not required, with the availability of new ELRS rxs that are RTF and have PWM outlets for servos laid out just like in older rxs.
These problems and solutions have been discussed at length on the PRCAC website "General Forum", which may be read by the public:
https://forum.rcflyingclub.com/forumdisplay.php?fid=3
Once these issues are addressed with the now fairly standard solutions, ELRS is simple to use and the advanced Edgetx tx software supports complex airplane setups with ease and precision. Edgetx is easier to use if you have previously used Opentx.
At PRCAC we were lucky to have an electronic whiz who quickly understood the issues and kindly made himself available to help other members (thanks Liam).
This article intends to describe what has happened at PRCAC, and is not an advertisement for particular brands. People who tried ELRS have became converts as their control signal issues became a thing of the past, indeed now most PRCAC members fly with ELRS.
A comparison of major RC radio brands - it may be the only one that is known or available - was posted in Aug 2023. The large and complex effort was undertaken by a Canadian RC enthusiast and blogger, "The Lighter Side of RC". It is discussed here:
https://forum.rcflyingclub.com/showthread.php?tid=1908
The comparison included Futaba, Spectrum, Frsky (tested with single band 2.4 Ghz rx, and a dual band rx (2.4 Ghz, 900 mhz)), Jeti (4 rx types), Radiomaster (boxer and Tx16s running ELRS), JR, and Powerbox. Radiomaster was the only brand on this list running ELRS.
RM/ELRS was the clear winner, even though it was placed at a disadvantage because ELRS's (arguably) best feature - dynamic power - was not used in the test. In second place was Frsky Tandem dual band. A detailed discussion of this comparison occurred on RC Groups: https://www.rcgroups.com/forums/showthre...comparison
This comparison had little effect on PRCAC as most people did not see it until 2024, by which time the majority of club members had decided to switch to an radio that ran ELRS, based on the experience of the early adopters. At PRCAC, Radiomaster has been the main choice for a ELRS tx, although there are a number of manufacturers such as Betafpv that produce ELRS modules that fit radios that have a module bay. Newcomers to ELRS usually want a tx that can run their existing rxs as well as their new ELRS rxs, and there are ways to achieve this using a module. Airplane-suitable ELRS ready-to-fly rxs are available from Radiomaster and Betafpv, whether you want 4, 6, 8, 14 or more channels.
ELRS has made an impact on every aspect of RC technology, and we have only covered some points and issues that may concern new adopters. A few additional advanced ELRS features like model match may be left turned off, until the pilot is more familiar with ELRS. We hope the experience with ELRS at PRCAC may encourage others pilots and clubs to check it out, especially if radio interference is an issue.
In April 2024 there are many excellent online guides for starting with ELRS:
Bardwell
https://www.youtube.com/watch?v=J3Hg2f7RL1A&t=1000s
RC Video Reviews
https://www.youtube.com/watch?v=AdgBoYJNI0M&t=1689s
Painless360
https://www.youtube.com/watch?v=q8NbnbLM9bE&list=PLYsWjANuAm4pbswfytdLD8MSjaX8YHfN1
Important further resources are:
https://www.expresslrs.org/ (this is a big website with many chapters that cover every aspect of ELRS)
https://discord.com/channels/59635002219...4762559488
(here, as on Radio Control Groups, you can post a question and an expert will respond usually within 24 hours)
Edgetx transmitter software for ELRS txs
https://manual.edgetx.org/
NOTES
1. ELRS Dynamic Power
ELRS has two transmission power modes, Dynamic and fixed. The Dynamic mode has a minimum value of 10mW or 25 mW, which is ample for line of sight flying, and jumps in power occur only when necessary. The ‘fixed’ mode outputs a fixed amount of power as selected by the user. The Dynamic mode allow us to maintain contact with our aircraft without outputting unnecessary power. We suggest always use the Dynamic Power mode, with the maximum boost power set to 100 or 150 mW for line of sight flying. Power above 150 or 250 mw is only used when flying fpv mode at distances greater than 5 or 10 km, or there is strong interference. Experience at PRCAC shows that power jumps rarely last more than 1-2 secs when interference strikes, and power then returns to the dynamic minimum.
2. Arming
ELRS requires that Ch 5 be turned on (or off) when you arm (or disarm) the motor of your aircraft. Ch 5 is not proportional like the other channels in ELRS, and is only ‘on’ or ‘off’. Arming is important because without it ELRS dynamic power is not fully functional.
The simplest arrangement is to assign Ch 5 to the same tx switch that you use to arm/disarm your motor. When the motor is disarmed with the switch, a special function on this switch sets Ch 5 to 0, and when the motor is armed, Ch 5 is set to 100. If you normally use Ch 5 for something else, we suggest set your old Ch 5 to Ch 6 (note that even a rx with 4 or 5 servo plugs has 8 or 16 channels with ELRS). When about to fly, the radio is first turned on with Ch 5 disarmed by the switch.
3. The Control and Telemetry Packets of the ELRS Radio Signal
Its true, most pilots just want to set and forget details like control and telemetry packets. ELRS provides amazing telemetry that encourages a pilot to understand many aspects of the radio signal and adjust it for their requirements. Few airplane pilots have previously set the telemetry ratio on their radio. It is useful to consider there are 2 sorts of packets in the radio signal, control packets going from the tx to rx, and simultaneously telemetry packets going from the rx to the tx. A telemetry packet and a control packet are both 10 millisecond duration. The following calculations are for a typical airplane ELRS setup of frequency 100 Hz and telemetry ratio 1:32. We can convert frequency units from hertz to millisecond (period), given that 100 Hz is 1 second or 1000 ms. If all the radio signal comprised telemetry packets, then telemetry would arrive at the tx at a rate of 1000/10 or 100 packets per second. But telemetry is only 1/32 of the signal. While the control packets are arriving at the rx at almost 100/sec, the telemetry packets are arriving at the tx at a rate 100/32 or 3.12 per sec.
This means: 3 times in every second, the rx sends a packet (a report) to the tx, containing data on the signal to noise ratio, the link quality, the number of packets the rx gets that are corrupt, the rx voltage, and more. If the tx computer considers the data together indicate a problem, with dynamic power the tx power is immediately raised (a power jump) to compensate. Some pilots set their tx to give a audio message whenever a power jump occurs.
Increasing radio signal problems when flying at the PRCAC field at Toongabbie have occurred over the last 3-4 years, coincident with the rapid development of 5G telecommunications in Sydney. PRCAC members mostly fly planes, and in 2022 they used a wide range of radio equipment with the 2.4 Ghz band, with almost all major RC brands represented. Near PRCAC is an Optus phone tower adjacent to our field and 40m from the landing strip, that uses many frequencies including the 2.35 Ghz band. However other possible suspects for interference are numerous nearby factories with networked computers, and also networked vehicle fleets.
Apart from crashes due to loss of control, or temporary control glitches, pilots occasionally noticed their aircraft take an unexpected change of direction and asked: was that me? Pilots paid increased attention to improved antennas, and better rxs and power supplies without much effect. A few members tried the 900 Mhz band, using gear such as Frsky R9 and Frsky Tandem; they reported 900 Mhz gear solved the problems, but 900 Mhz never became popular at PRCAC.
Around Oct 2022 a trusted radio expert on Radio Control Groups said ELRS "is really a sea change in the available RF performance for 2.4 Gz systems and a major shot across the bows of the older solutions, especially for those of us flying in more challenging RF environments". This post and similar discussions on Radio Control Groups encouraged several PRCAC members to try ELRS, even though the general perception at the time was that ELRS was a drone radio.
In a nutshell: ELRS evolved because fpv drone pilots wanted to fly at long distances say 20 km and return safely. The ELRS developers discovered how to maintain a safe signal to noise ratio at a distance, and out of early prototypes such as Crossfire and Ghost there emerged ELRS. Turns out, the amazing signal to noise performance of ELRS is just what pilots of "fixed wing" (what drone pilots call airplanes) need at a 200 m distance to counter radio interference.
The ELRS early adopters at PRCAC experienced problems due to numerous differences between ELRS and commonly used radios such as Frsky or Spectrum; while each difference has a simple solution, there are around 6 to consider and address:
- running the Configurator on a computer to update tx or rx firmware.
- flashing tx or rxs with updated firmware using the internet and wifi; wifi is also used to set the tx and rx "bindphrase", which allows instant tx to rx binding when the tx and rx have a match.
- understanding the control and telemetry packets of the radio signal (see Notes below). For aircraft flown with line of sight, a packet rate 100 Hz, and a telemetry ratio of 1:32 are recommended.
- setting "dynamic power", so if interference corrupts the radio signal, the tx power immediately jumps say from 25 to 50 mw.(see Notes below)
- "arming" and channel 5 setting. Some think arming is only for drones, but that is not true. Dynamic power performance is enhanced if armed. (see Notes below)
- soldering wires onto rx boards. This was an early problem for some members, but now is not required, with the availability of new ELRS rxs that are RTF and have PWM outlets for servos laid out just like in older rxs.
These problems and solutions have been discussed at length on the PRCAC website "General Forum", which may be read by the public:
https://forum.rcflyingclub.com/forumdisplay.php?fid=3
Once these issues are addressed with the now fairly standard solutions, ELRS is simple to use and the advanced Edgetx tx software supports complex airplane setups with ease and precision. Edgetx is easier to use if you have previously used Opentx.
At PRCAC we were lucky to have an electronic whiz who quickly understood the issues and kindly made himself available to help other members (thanks Liam).
This article intends to describe what has happened at PRCAC, and is not an advertisement for particular brands. People who tried ELRS have became converts as their control signal issues became a thing of the past, indeed now most PRCAC members fly with ELRS.
A comparison of major RC radio brands - it may be the only one that is known or available - was posted in Aug 2023. The large and complex effort was undertaken by a Canadian RC enthusiast and blogger, "The Lighter Side of RC". It is discussed here:
https://forum.rcflyingclub.com/showthread.php?tid=1908
The comparison included Futaba, Spectrum, Frsky (tested with single band 2.4 Ghz rx, and a dual band rx (2.4 Ghz, 900 mhz)), Jeti (4 rx types), Radiomaster (boxer and Tx16s running ELRS), JR, and Powerbox. Radiomaster was the only brand on this list running ELRS.
RM/ELRS was the clear winner, even though it was placed at a disadvantage because ELRS's (arguably) best feature - dynamic power - was not used in the test. In second place was Frsky Tandem dual band. A detailed discussion of this comparison occurred on RC Groups: https://www.rcgroups.com/forums/showthre...comparison
This comparison had little effect on PRCAC as most people did not see it until 2024, by which time the majority of club members had decided to switch to an radio that ran ELRS, based on the experience of the early adopters. At PRCAC, Radiomaster has been the main choice for a ELRS tx, although there are a number of manufacturers such as Betafpv that produce ELRS modules that fit radios that have a module bay. Newcomers to ELRS usually want a tx that can run their existing rxs as well as their new ELRS rxs, and there are ways to achieve this using a module. Airplane-suitable ELRS ready-to-fly rxs are available from Radiomaster and Betafpv, whether you want 4, 6, 8, 14 or more channels.
ELRS has made an impact on every aspect of RC technology, and we have only covered some points and issues that may concern new adopters. A few additional advanced ELRS features like model match may be left turned off, until the pilot is more familiar with ELRS. We hope the experience with ELRS at PRCAC may encourage others pilots and clubs to check it out, especially if radio interference is an issue.
In April 2024 there are many excellent online guides for starting with ELRS:
Bardwell
https://www.youtube.com/watch?v=J3Hg2f7RL1A&t=1000s
RC Video Reviews
https://www.youtube.com/watch?v=AdgBoYJNI0M&t=1689s
Painless360
https://www.youtube.com/watch?v=q8NbnbLM9bE&list=PLYsWjANuAm4pbswfytdLD8MSjaX8YHfN1
Important further resources are:
https://www.expresslrs.org/ (this is a big website with many chapters that cover every aspect of ELRS)
https://discord.com/channels/59635002219...4762559488
(here, as on Radio Control Groups, you can post a question and an expert will respond usually within 24 hours)
Edgetx transmitter software for ELRS txs
https://manual.edgetx.org/
NOTES
1. ELRS Dynamic Power
ELRS has two transmission power modes, Dynamic and fixed. The Dynamic mode has a minimum value of 10mW or 25 mW, which is ample for line of sight flying, and jumps in power occur only when necessary. The ‘fixed’ mode outputs a fixed amount of power as selected by the user. The Dynamic mode allow us to maintain contact with our aircraft without outputting unnecessary power. We suggest always use the Dynamic Power mode, with the maximum boost power set to 100 or 150 mW for line of sight flying. Power above 150 or 250 mw is only used when flying fpv mode at distances greater than 5 or 10 km, or there is strong interference. Experience at PRCAC shows that power jumps rarely last more than 1-2 secs when interference strikes, and power then returns to the dynamic minimum.
2. Arming
ELRS requires that Ch 5 be turned on (or off) when you arm (or disarm) the motor of your aircraft. Ch 5 is not proportional like the other channels in ELRS, and is only ‘on’ or ‘off’. Arming is important because without it ELRS dynamic power is not fully functional.
The simplest arrangement is to assign Ch 5 to the same tx switch that you use to arm/disarm your motor. When the motor is disarmed with the switch, a special function on this switch sets Ch 5 to 0, and when the motor is armed, Ch 5 is set to 100. If you normally use Ch 5 for something else, we suggest set your old Ch 5 to Ch 6 (note that even a rx with 4 or 5 servo plugs has 8 or 16 channels with ELRS). When about to fly, the radio is first turned on with Ch 5 disarmed by the switch.
3. The Control and Telemetry Packets of the ELRS Radio Signal
Its true, most pilots just want to set and forget details like control and telemetry packets. ELRS provides amazing telemetry that encourages a pilot to understand many aspects of the radio signal and adjust it for their requirements. Few airplane pilots have previously set the telemetry ratio on their radio. It is useful to consider there are 2 sorts of packets in the radio signal, control packets going from the tx to rx, and simultaneously telemetry packets going from the rx to the tx. A telemetry packet and a control packet are both 10 millisecond duration. The following calculations are for a typical airplane ELRS setup of frequency 100 Hz and telemetry ratio 1:32. We can convert frequency units from hertz to millisecond (period), given that 100 Hz is 1 second or 1000 ms. If all the radio signal comprised telemetry packets, then telemetry would arrive at the tx at a rate of 1000/10 or 100 packets per second. But telemetry is only 1/32 of the signal. While the control packets are arriving at the rx at almost 100/sec, the telemetry packets are arriving at the tx at a rate 100/32 or 3.12 per sec.
This means: 3 times in every second, the rx sends a packet (a report) to the tx, containing data on the signal to noise ratio, the link quality, the number of packets the rx gets that are corrupt, the rx voltage, and more. If the tx computer considers the data together indicate a problem, with dynamic power the tx power is immediately raised (a power jump) to compensate. Some pilots set their tx to give a audio message whenever a power jump occurs.